WASHINGTON — The searing portrait that Michael D. Cohen delivered on Wednesday — of a lying, cheating, racist president who used money and threats to conceal immoral and illegal behavior — will test both parties as they hurtle toward a confrontation over the fate of the presidency.
Mr. Cohen, President Trump’s former personal lawyer, ripped away the veneer of loyalty that he had maintained for more than a decade and further imperiled the president by offering an insider account at the heart of the criminal investigations that have consumed Washington for nearly two years.
The five-hour hearing offered a glimpse of a confrontational year ahead between Republicans still loyal to Mr. Trump and newly empowered Democrats seeking to investigate and weaken the president by demanding his tax returns and business records, and appearances before Congress by his former advisers and associates.
But the year will also be a test for both parties, particularly Democrats, who after Wednesday’s testimony from Mr. Cohen will face a rising chorus from the liberal wing of the party to impeach Mr. Trump for what it says is a clear case of a president who defrauded the public about hush payments and business dealings before an election and then lied about it from the White House.
“Mr. Cohen, I am upset and know that my residents feel the same way, that a man you worked for for the past 10 years is using the most powerful position in the world to hurt our country solely for personal gain,” said Representative Rashida Tlaib, Democrat of Michigan.
Faced with that pressure, how long will Democratic leaders be able to argue against impeachment proceedings? And if they move ahead, with little hope of attracting bipartisan support, will they risk a backlash at the polls from voters?
“The more you do this, it just fires up the base that thinks that each day he stays in office it endangers the republic,” said Thomas M. Davis, a former Republican congressman from Virginia who once led the Oversight Committee when his party controlled the House. “It’s the old thing about be careful what you ask for.”
For Republicans, Mr. Cohen’s allegations will once again require Mr. Trump’s followers to decide how long they will stand by a president whose actions threaten not only his administration but also the fate of politicians in the party he now leads.
Republican lawmakers on the committee reacted to Mr. Cohen’s testimony with derision, attacking him as a convicted perjurer, a Democratic patsy, a liar and a cheat. And yet, as Mr. Cohen noted in one of the most powerful moments of the day, their fierce loyalty to Mr. Trump was not unlike his own.
“I’m responsible for your silliness because I did the same thing that you’re doing now, for 10 years,” Mr. Cohen said. “I protected Mr. Trump for 10 years. I can only warn people — the more people that follow Mr. Trump as I did blindly, are going to suffer the same consequences that I’m suffering.”
Yet Republicans on the panel from conservative districts have little to lose. Representatives Mark Meadows of North Carolina and Jim Jordan of Ohio, who harshly criticized Mr. Cohen as a liar headed to prison, appeared to play to the many faithful Trump voters at home, not to mention the president himself. They seemed to conclude that the best way to support Mr. Trump was by attacking Mr. Cohen’s credibility. They did so repeatedly, each lawmaker returning to the same accusation each time the chance arose: Why should we believe someone who is going to jail for lying to us before?
“They accomplished what they wanted to,” David Axelrod, the former senior adviser to President Barack Obama, said of the Republicans on the committee. “The more that they polarize this and present it as a political exercise, the more everyone runs to the red corner and blue corner. And Trump sits there very popular with the base.”
He added, “The Republicans are making a political decision about the cost of sticking with him.”
Mr. Cohen’s appearance, broadcast live on cable networks, was a political milestone with echoes of the 1973 congressional testimony by John Dean, Richard M. Nixon’s White House counsel, whose admission that he discussed the Watergate cover-up with Nixon dozens of times helped drive the embattled president from office 14 months later.
The power of Mr. Cohen’s testimony on Wednesday was less about the details in his answers, even though he revealed some new information that Democrats seized on as further proof of presidential misdeeds.
Instead, what Mr. Cohen offered to the committee was a highly personal narrative and the kind of insider description largely missing from the legal documents of federal prosecutors.
Mr. Cohen recounted the time, for example, that Mr. Trump mentioned that he was reimbursing him for hush payments Mr. Cohen made to a pornographic film actress even as he gave Mr. Cohen his first tour of the Oval Office.
“He’s showing me all around and pointing to different paintings,” Mr. Cohen said during his opening statement, his words echoing through the hearing room. “And he says to me something to the effect of: ‘Don’t worry, Michael. Your January and February reimbursement checks are coming.’”
Mr. Cohen also recounted an incident in a car when Mr. Trump called Mr. Cohen and then handed the phone to Melania Trump, his wife, so that his lawyer could falsely deny to Mrs. Trump that Mr. Trump had had an affair.
“That was my job. Always stay on message. Always defend,” said Mr. Cohen, who once said he would take a bullet for Mr. Trump.
It is unclear how Mr. Cohen’s testimony — alternately self-confident, exasperated, ashamed — will reverberate inside the two political parties, whose most partisan and committed voters view Mr. Cohen and Mr. Trump through radically different prisms.
Mr. Axelrod, who has spent much of his life helping to craft effective political messages, said the highly personal nature of Mr. Cohen’s testimony — including accusations that the president is a racist — may have detracted from the effectiveness.
“His statement would have been more damning or damaging if it were slightly less personal. It seemed like a catharsis for him,” Mr. Axelrod said, noting the many gratuitous asides that Mr. Cohen seemed to relish in delivering for the cameras. “Maybe that is a product of his frustration.”
Mr. Davis said he thought Mr. Cohen’s testimony would do little to change the political dynamic in the country.
“A lot of this stuff is baked in the cake,” he said, talking about his colleagues in the Republican Party. “People accept him regardless of what some would call character flaws.”